Basing her story on the published accounts of her true-life heroine, Mary Ellen Todd, Van Leeuwen (Going West; the Oliver and Amanda Pig series) describes a family's tumultuous journey along the Oregon Trail in 1852. En route to a ``beautiful land of promise,'' nine-year-old Mary Ellen, her two sisters and her father and stepmother find themselves beset by all manner of dramas, from the dog being allowed an unprecedented ride in the wagon when his paws are sore to a near-fatal brush with cholera and an attack by Indians. Mary Ellen's first-person narration is innocent, fresh and heartfelt (``Never, I thought, had I seen a world so large,'' she says of the plains of Nebraska), and capable of conveying darker feelings as well. She is ``furious'' with her father for imperiling his family; when her stepmother frowns at her for dirtying her dress, she thinks, ``My real mother wouldn't care about a few grass stains.'' The novel ends on a sweet note, however, with the birth of a baby and the celebration of Christmas, when each family member thanks God for the family's safe arrival in Oregon (``I am thankful that Blackie gave us milk all the way through''). The contrast between the tenderness of Mary Ellen's perceptions and the hardships of the frontier is deeply moving. Ages 8-12. (Oct.)